tracking warp stabilized footage

I have a piece of HD video in PPro that's a guy driving in a car, talking to the camera. I took advantage of the new warp stabilize feature in AE 5.5 to steady the shot. It worked like a charm. But now I need to mask a window in the vehicle to drop the levels a bit to even out the shot. In a perfect world, I would parent the mask I've created to some parameter in the Warp Stabilizer effect, but I don't see anything keyframeable in there. Can I do this? How?